C99

ISO/IEC 9899:1999, a.k.a. C99, is a previous revision of the C standard.

Obsolete

Removed

• Implicit int in declarations
• Implicit function declarations

Deprecated

• gets()

New language features

• Universal-character-names in identifiers
• Increased translation limits
• // comments
• restrict pointers
• Enhanced arithmetic types
  • _Bool
  • long long and unsigned long long
  • Extended integer types
  • _Complex types (float _Complex, double _Complex, and long double _Complex)
  • _Imaginary types (float _Imaginary, double _Imaginary, and long double _Imaginary)
• Flexible array members
• Variable-length array (VLA) types and variably-modified (VM) types
• Improvements of braced-init-list for array, struct and union types
  • Non-constant initializers
  • Designated initializers
• Idempotent cvr-qualifiers
• Trailing comma in enumerator-list
• Hexadecimal floating constants
• Compound literals
• Floating-point environment
• Requiring truncation for divisions of signed integer types
• Implicit return 0; in the main() function
• Declarations and statements in mixed order
• init-statement in for loops
• inline functions
• Predefined variable __func__
• Cvr-qualifiers and static in [] within function declarations
• Variadic macros
• _Pragma preprocessor operator
• Standard pragmas for floating-point evaluation
  • STDC FENV_ACCESS
  • STDC FP_CONTRACT
  • STDC CX_LIMITED_RANGE

Feature test macros for optional features

• __STDC_IEC_559__
  • Indicates IEEE-754 binary floating-point arithmetic and required math functions are supported.
• __STDC_IEC_559_COMPLEX__
  • Indicates IEEE-754 complex arithmetic and required math functions are supported.
• __STDC_HOSTED__
  • Indicates that the implementation is hosted.
• __STDC_ISO_10646__
  • Indicates that Unicode is used by the wide literal encodings and expands to the latest supported revision.
• __STDC_MB_MIGHT_NEQ_WC__
  • Indicates that there are some characters in the basic character set having different code unit values in ordinary and wide literal encodings.

New library features

New headers

• <complex.h>
• <fenv.h>
• <inttypes.h>
• <stdbool.h>
• <stdint.h>
• <tgmath.h>

Library features

• Aliases for integer types
  • Integer types with exact width (intN_t and uintN_t)
  • Fastest integer types with at least given width (int_fastN_t and uint_fastN_t)
  • Smallest integer types with at least given width (int_leastN_t and uint_leastN_t)
  • Integer types capable for cast between object pointers (intptr_t and uintptr_t)
  • Integer types with maximum width (intmax_t and uintmax_t)
• Operations on long long and intmax_t
  • llabs()
  • imaxabs()
  • lldiv()
  • imaxdiv()
• Floating-point environment access
• Extended floating-point math functions
  • New floating-point math functions
  • -f and -l variants for existing and new floating-point math functions
  • Math error handling
• Complex functions
• _Exit()
• Formatting support for long long, unsigned long long, intmax_t, and uintmax_t
  • atoll()
  • strtoimax()
  • strtoll()
  • strtoull
  • strtoumax()
  • wcstoimax()
  • wcstoll()
  • wcstoull()
  • wcstoumax()
• isblank() and iswblank()
• snprintf() and vsnprintf()
• vfscanf() and vfwscanf() function families
• Extensions for fscanf() and fprintf() function families
  • ll length modifier for long long and unsigned long long
  • hh length modifier for signed char and unsigned char
  • l length modifier for double
  • z length modifier for size_t and its signed version
  • t length modifier for ptrdiff_t and its unsigned version
  • j length modifier for intmax_t and uintmax_t
  • a conversion specifier for floating-point types
• Numeric limit macros for long long and unsigned long long
• Numeric limit macros corresponding to existing and new aliases for integer types
• Format string macros for integer types
• va_copy
• Type-generic math macros
• Floating-point comparison macros
• Floating-point classification macros
• Compatibility macros for _Bool (bool, true, and false)

Defect reports

Template:c/language/history/DR99.

Compiler support

C99 core language features